It's called UemeU (pronounced "You Me You"). It's currently in development for PC. And, uh... I'm not entirely sure what it is.

I mean, I see that you're supposed to build stuff with it. The video shows the developers building a bare-bones version of Erebor from The Hobbit. But it's not just building, there's modelling involved, too. Look at this:

Animation. So is it a game or a modelling tool? Both, apparently—they say it's a community-driven multiplayer sandbox inspired by Minecraft, Garry's Mod, Little Big Planet, and The Sims. It's like they took the sandbox elements from all these games to create the sandboxiest of sandboxes.

UemeU does look at least as weird as Garry's Mod, undoubtedly the strangest of the inspirations named, but it's more of an abstract weird, judging by the videos. You don't create outlandish things using pre-existing objects, but rather, you create the objects themselves, and then build outlandish things using your own newly-made objects. Interesting!